1. Field of the Invention.
The present invention relates to a vortex flowmeter and more particularly to a sensor for use with a vortex flowmeter utilizing a beam that provides a flow-related output by pivoting or rocking in response to vortex induced differential pressures on a sensing diaphragm.
2. Description of the Prior Art.
Various differential pressure sensitive vortex flowmeters have been advanced which operate on the principle that a bluff body or bar placed in a fluid flow will cause a generation of vortices alternately on opposite sides of the bluff body, causing variations in pressure downstream from the bar. The frequency of vortex shedding is found to be directly proportional to the velocity of flow in the stream for an individual bar configuration characteristic. Twin diaphragm differential pressure sensors used with vortex shedding bluff bodies have been advanced, as shown in U.S. Pat. No. 4,475,405. Deflections of the diaphragm in turn will cause bending of a sensing beam. Twin diaphragm sensors have been found to be sensitive to fluctuations in the static line pressure unless the diaphragms are exactly matched and remain matched under the influence of static pressure. This has practical limitations. Double diaphragm systems with an intermediate fluid fill have been used, but problems with high temperature operation limit performance. Single diaphragms heretofor have been impractical because the use of sensors on a single diaphragm would require exposure of the sensors to the fluid being sensed, and most industrial process fluids will damage sensors.
One measure of the ability of a sensor to reject variations in static pressure is called the common mode rejection ratio. This is defined as the ratio of the sensor output per unit of differential pressure to the output of the sensor per unit of common mode (static) pressure. This ratio should be very large, preferably greater than 2000.